Psora pseudorussellii
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| Psora pseudorussellii | |
|---|---|
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Scientific classification  | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Lecanoromycetes |
| Order: | Lecanorales |
| Family: | Psoraceae |
| Genus: | Psora |
| Species: | P. pseudorussellii |
| Binomial name | |
| Psora pseudorussellii Timdal (1987) | |
Psora pseudorussellii, the bordered scale, is a species of rock-dwelling squamulose lichen in the family Psoraceae.[2] It forms patches of small, brown, scale-like structures with distinctive white margins on limestone and other calcareous rocks in eastern and southern North America, from southeastern Canada south into Mexico. The species was described in 1986 to separate it from similar material that had been confused with Psora russellii, and DNA studies have confirmed that it is restricted to North America, with European and Asian specimens previously identified as this species actually representing different taxa.
Psora pseudorussellii was described as a new species by Einar Timdal in 1986, during his revision of North American Psora. In that treatment, Timdal separated it from material that had often been filed under Psora russellii, clarifying that two different taxa were being mixed under a single name in eastern North America.[3]
The species is closely related to P. tuckermanii and can be difficult to tell from it in some collections. Timdal distinguished P. pseudorussellii by its generally smaller, darker brown squamules with a more distinctly white margin, and by its young apothecia, which tend to be more reddish brown, less strongly convex, and more clearly marginate. He also emphasized ecology: P. pseudorussellii is strictly saxicolous, while P. tuckermanii occurs on both rock and soil.[3]
Molecular work published in 2025 supported Timdal's concept of Psora pseudorussellii and provided the first publicly available internal transcribed spacer (ITS) barcode sequences from North American material. The same study found that European collections previously identified as P. pseudorussellii represent a separate Mediterranean species, described as Psora mediterranea, and that sequences published as "P. cf. pseudorussellii" from China are better interpreted as P. himalayana. As a result, reports of P. pseudorussellii from outside North America should be treated with caution unless they are supported by modern revision work or DNA data.[4]